1. Field of the Invention
This invention relates to a magneto-optical recording medium for recording information by use of a laser beam, and particularly to a magneto-optical recording medium which has a high magneto-optic effect under a short-wavelength light and is suitable for high-density recording.
2. Description of the Prior Art
Magneto-optical recording has been put to practical use through a rewritable optical recording approach. Until now, a single amorphous rare-earth-transition-metal film with a strong magnetic anisotropy in the direction perpendicular to the film surface has been used as a magneto-optical recording film. In particular, TbFeCo alloy system amorphous films have been researched and developed for practical use. In magneto-optical recording, there is a trend toward higher recording density, and use of a short-wavelength read/write light is now being researched as a possible approach. For this purpose, the development of magneto-optical materials with higher magneto-optic effects (Kerr rotation and Faraday rotation) is essential in order to achieve higher density magneto-optical recording in the future.
However, in the conventional TbFeCo alloy series amorphous film, as the wavelength of the laser beam becomes shorter, the magneto-optic effect tends to decrease monotonically. Thus, a sufficiently large Kerr rotation angle or Faraday rotation angle cannot be obtained at short wavelengths, and thus there is a problem that the output in reading with the laser beam decreases greatly. It was recently proposed that a two-layer film be used as a new magneto-optical film with magnetic exchange coupling between layers (for example, see Japanese Published Unexamined Patent Application No. 60-171652). However, since these are also substantially TbFe alloy system laminated films, the Kerr rotation angle decreases at short wavelengths. They are therefore unsuitable for read/write films at short wavelengths.
On the other hand, a rare-earth-transition-metal amorphous film consisting mainly of Nd or Pr is known (for example, see T. R. McGuire et al., "Magneto-optical Properties of Nd-Co and Nd-Fe alloys", J. Appl. Phys. 61 (1987) pp. 3352-3354). Although this film has a characteristic higher magneto-optical effect at short wavelengths, it is not a perpendicular magnetized film with strong magnetic anisotropy in the direction perpendicular to the film surface, but merely an in-plane magnetized film with strong magnetic anisotropy in the direction parallel to the film face. Thus, high-density recording cannot be attained.